Normal oxyhemoglobin saturation during sleep - How low does it go?

Study objective: To determine oxyhemoglobin saturation (O-2 Sat) in healthy humans. Design: Retrospective review of all-night pulse oximetry data, carefully examined to exclude periods of motion artifact. The lowest saturation recorded during the night (Low Sat), the median saturation (Sat 50), and the saturation below which the patient spent 10% of the time (Sat 10) were tabulated, These data were compared to the O-2 Sat in patients with obstructive sleep apnea (OSA) and patients with stable asthma. Setting: Sleep laboratory in a tertiary care hospital. Patients: Three hundred fifty people with normal results of overnight polysomnography. Patients with known craniofacial or neurologic abnormalities or any previously diagnosed pulmonary disease such as asthma or COPD were excluded. The healthy subjects ranged in age from 1 month to 85 years, There were 184 male and 166 female subjects, These were compared to 25 patients with OSA and 21 patients with asthma, Results: For the healthy patients, the mean +/- SD Low Sat was 90.4% +/- 3.1%, The mean Sat 10 was 94.7% +/- 1.6%. The mean Sat 50 was 96.5% +/- 1.5%, There was no relationship between any of the O-2 Sat measures and sex, race, or obesity as measured by body mass index. However older subjects (> 60 years of age) had lower Sat 10 (92.8 +/- 2.3) and Sat 50 (95.1 +/- 2.0) than did younger subjects, The O-2 Sat of the patients with asthma was not different from the healthy subjects, but the patients with OSA had a significantly lower Sat 50, Sat 10, and Low Sat. Summary: We describe in detail O-2 Sat in a large group of healthy people, Older subjects without known cardiorespiratory disease have lower O-2 Sat than younger subjects.